linux-kernel - Re: Time: new clocksource

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Message-ID: <CAHhAz+izC=8ZbkxpbveS1u3Va1kwdCC4j4cEgMmRFojY-it+Rw@mail.gmail.com>
Date:   Mon, 6 Dec 2021 12:30:54 +0530
From:   Muni Sekhar <munisekharrms@...il.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     tglx@...utronix.de, LKML <linux-kernel@...r.kernel.org>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>
Subject: Re: Time: new clocksource

On Mon, Dec 6, 2021 at 11:59 AM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> On 06/12/2021 07:00, Muni Sekhar wrote:
> > On Sat, Dec 4, 2021 at 3:18 AM Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
> >>
> >> Hi Sekhar,
> >>
> >> On 03/12/2021 17:50, Muni Sekhar wrote:
> >>> Hi All,
> >>>
> >>> We have a Digital PLL with 64 bit timer counter hardware and the
> >>> counter is accessible from the CPU over the PCIe bus.
> >>>
> >>> Is it possible to add this timer counter hardware as new clocksource
> >>> driver? To do this, can someone please point me to the existing
> >>> reference source code(or patch) for this task.
> >>
> >> You can refer to the drivers located in drivers/clocksource
> > I don't see the option in menuconfig to build the clocksource driver
> > as a loadable kernel module, for example CONFIG_X86_PM_TIMER=m instead
> > of CONFIG_X86_PM_TIMER=y.
> > So a clocksource driver should always be part of the kernel built-in
> > module?
>
> Yes, that is the case today.
>
> > If so, what's the reason for that?
>
> The timer is a component needed at boot time, so a module version does
> really not make sense.
>
> So I would return back the question : what is the reason for a module?
For built-in module we need to compile the whole kernel, but we are
currently using the kernel via linux-image-4.15.0-54-generic.deb file
installation.
>
>
> >> git annotate on one of the driver can give you the initial commit where
> >> recent submissions explain the timer internals.
> >>
> >>> Suppose if it is possible to add a new clocksource driver for this
> >>> hardware then does any userspace get_timestamp* API would get the time
> >>> from this new hardware?
> >>
> >> It should if the timer is selected as the clocksource
> >>
> >>
> >> --
> >> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
> >>
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> >
> >
> >
>
>
> --
> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
>
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-- 
Thanks,
Sekhar